1. Field of the Invention
This invention relates to vibration-controlling bearings having high vibration damping capabilities, and, more particularly, to a vibration-controlling bearing suitable for use as a low-load bearing for a rotary machine of the compact size and high speed rotation type having a bearing surface lubricated by a fluid filled around the bearing.
2. Description of the Prior Art
Generally, in a slide bearing lubricated by a fluid, a film of fluid, formed in a gap between the bearing surface and the rotary shaft, as the rotary shaft rotates, excites the shaft at high speed rotation, thereby causing unstable vibration generally referred to as a whirl to be produced. Various proposals have been made to use different types of slide bearing to suppress the unstable vibration, and some of them have been put to practical use.
Typical of the known vibration-controlling bearings include a tilting pad bearing and a damper bearing such as disclosed, for example, in Japanese patent publication No. 22607/78. This type of bearing has a construction essentially enabling the exciting action of a fluid film to be eliminated, so that the difficulty of unstable vibration sets in until rotation of the shaft reaches a high speed range. However, it suffers the disadvantages that the construction is complex and the cost is high. A damper bearing has been developed for the purpose of obviating the disadvantages of the tilting pad bearing which is essentially constructed in a manner to softly mount a radial slide bearing member in a housing through support means having a spring action and a damping action. The support means of this type has the function of alleviating and absorbing a force tending to excite a fluid film formed between the shaft and the bearing member, so that unstable vibration can be prevented from developing in the shaft until rotation of the shaft reaches a high speed rotation range. The support means of this type comprising a spring, such as a coil spring or plate spring, and a damper, including a viscous fluid located on the outer periphery of the bearing member and in the gap between the housing and the bearing member, has been put to practical use in some type of machines. However, like the tilting pad bearing, the damper bearing is also complex in construction and high in cost, so that its use is limited. Meanwhile a floating bush bearing is available which, although it is one type of damper bearing, is relatively simple in construction and low in cost. The floating bush, bearing comprises a bush of the cylindrical shape and having a plurality of radial oil feed openings, loosely fitted between the shaft and the housing for receiving a supply of fluid from outside fluid feeding means into a gap between the inner surface of the bush and the shaft and a gap between the outer surface of the bush and the housing for lubrication, so that the bush can be rotated by the viscous resistance of the lubricating fluid on the inner surface of the bush as the shaft rotates to thereby form a lubricating film of fluid between the outer surface of the bush and the housing. The lubricating film of fluid on the outer surface of the bush has both the spring action and the damping action, so that it is capable of alleviating and absorbing a force tending to excite the film of fluid on the inner surface of the bush. This type of bearing has been put to practical use as a high-speed bearing of relatively low load, such as a bearing used with a turbo supercharger. In actual practice, however, this type of bearing suffers the disadvantage that stable rotation of the bush is unobtainable. Thus, formation of a fluid film on the outer surface of the bush does not occur in a stable manner, with the result being that it is not possible to completely suppress unstable vibration of the shaft. Particularly when the lubricating fluid used is a low-viscosity fluid, such as water or gas, it is practically impossible to achieve stable rotation of the bush because a rotary force developing from the viscous resistance of the fluid film acting on the inner side of the bush is low. This defect would be considered fatal from the point of view of maintaining reliability of the machine.